I means Tôi:

Tôi is used to refer to you in formal way

You: we have a lot of Vietnamese words to translate the word YOU ( Anh, Chị, Em, Ông, Bà, Cô, Bạn….) depending on many things such as sex, age, the relationship between the speaker and thelistener.

Anh:

is used when addressing a young male or a male who is at the same age (politely) or a bit older than you

Chị:

is used when addressing a young female or a female who is at the same age (politely) or a bit older than you

Em:

is used when addressing children, both male or female, or anybody younger than you are)

Ông:

is used when addressing an old man, about or over 50 years old, can be translated as Mr or Sir)

Bà

is used when addressing an old woman or a married woman

Cô: (Miss)

is used when addressing a young female

Bạn:

is used when addressing a friend or  young girl, young man (informal, intimate)